Sm2(Co,Cu,Fe,Zr)17 are the best high-temperature permanent magnets because of their high Curie temperature (800°C–850°C). However, irreversible and unacceptable coercivity losses retard their use in applications at temperatures over 550°C. The coercivity loss has been correlated with poor oxidation resistance at high temperatures. The current research progress on the effect of oxidation and its prevention, for 2:17-type magnets, is reviewed. Oxidation in air at 500°C–700°C causes the magnets to form three regions: (1) an external oxide scale mainly consisting of (CoxFe1-x)3O4, (2) a thicker internal oxidation zone where the typical cellular precipitation (2:17R cell and 1:5H cell boundary) structure has been completely collapsed due to the Sm oxidation into Sm2O3, and (3) an oxidation-free zone where the cellular precipitates remain unchanged in lattice structure. No unacceptable coercivity loss is seen in the oxidation-free zone. Its thickness can be impressively increased within the magnets at high temperature, when they are covered with surface diffusion barriers for oxygen from the atmosphere, such as thin films of Cr2O3, Al2O3, and the metals with the ability to thermally grow these oxides.
About the authors
Xiao Peng obtained his PhD degree in Corrosion and Protection at the Institute of Corrosion and Protection of Metals, Chinese Academy of Sciences. He was a post-doctorate researcher at the Materials Department of the University of California at Santa Barbara from 1998 to 1999 and a visiting scientist at the Chemistry Department of Western Kentucky University from 1999 to 2001. He has been a Professor at Institute of Metal Research, Chinese Academy of Sciences, since 2001. He has 25 years’ experience in high-temperature corrosion and protection of metallic materials. He has published over 100 peer-reviewed journal articles and over 10 invited presentations for international conferences.
Hongbo Zhao studied Metallurgical Science and Engineering at the Central South University of China between 2006 and 2010. In 2010, he was recommended to work on his PhD degree in corrosion and protection of metals without exams under Prof. Xiao Peng’s guidance at Institute of Metal Research, Chinese Academy of Sciences. He is currently doing his PhD research mainly on high-temperature oxidation and protection of samarium-cobalt permanent magnets.
Xiaolan Wang received her Master’s degree in Materials Science from the Institute of Metal Research, Chinese Academy of Sciences, in 2005. She is currently an engineer at the Institute of Metal Research and pursuing a PhD degree. Her current research focuses on the understanding of high-temperature oxidation of materials in terms of TEM studies.
Zhaohui Guo received his MS degree in Condensed Matter Physics at the Institute of Physics, Chinese Academy of Sciences, in 1996. Then he joined the Division of Functional Materials at the Central Iron and Steel Research Institute, where he obtained his PhD in Materials Science and engineering in 2006. He is currently a Professor at the institute, responsible for R&D on high-temperature rare earth permanent magnets and nanocomposite permanent magnets. Dr. Guo has more than 20 years’ experience and has published over 40 technical articles on rare earth magnets. He has obtained several National Scientific and Technological Progress Awards of China.
Wei Li studied Magnetism at Shandong University between 1978 and 1982. Since 1984, he has been a Professor at the Central Iron and Steel Research Institute, doing research on the microstructure, magnetic, mechanical, and corrosion properties of rare earth permanent magnetic materials. He has over 30 years’ experience and has published over 150 articles. He is an elected member of the Asia Pacific Academy of Materials and a director of the Chinese Society of Rare Earths. He won one First-Class Prize and two Second-Class Prizes for National Scientific and Technological Progress Awards of China.
Fuhui Wang received his PhD in Corrosion and Protection at Institute of Corrosion and Protection of Metals, Chinese Academy of Sciences, in 1992. He was a deputy director of Institute of Corrosion and Protection of Metals and the director of State Key Lab for Corrosion and Protection. He worked at the Technical University of Munich, Germany, for 1 year and at University of New South Wales, Australia, for 6 months. He is a Professor at the Institute of Metal Research and is the president of the Chinese Society for Corrosion and Protection. His main research interests are high-temperature corrosion and protection, particularly on coating development and synergistic effect of NaCl and water vapor on metal corrosion.
The work is supported by National Basic Research Program (No. 2010CB934604) of China, Ministry of Science and Technology.
Bein S, Colinet C, Durand-Charre M. CVM calculation of the ternary system Co-Cu-Fe. J Alloys Compd 2000; 313: 133–143.10.1016/S0925-8388(00)01198-1Search in Google Scholar
Böhm G, Kahlweit M. Uber die innere oxydation von metallegierungen. Acta Metall Mater 1964; 12: 641–648.10.1016/0001-6160(64)90036-7Search in Google Scholar
Chen CH, Walmer MS, Walmer MH, Liu S, Kuhl EG, Simon G. Sm2(Co,Fe,Cu,Zr)17 magnets for use at temperature ≥400°C. J Appl Phys 1998; 83: 6706–6708.10.1063/1.367937Search in Google Scholar
Chen CH, Walmer MS, Walmer MH, Liu S, Kuhl EG. Thermal stability of Sm-TM high temperature magnets at 300–550°C. IEEE Trans Magn 2000; 36: 3291–3293.10.1109/20.908773Search in Google Scholar
Chen CH, Walmer MH, Kottcamp EH, Gong W. Surface reaction and Sm depletion at 500°C. IEEE Trans Magn 2001; 37: 2531–2533.10.1109/20.951225Search in Google Scholar
Chen C, Walmer MH, Liu S. Thermal stability and the effectiveness of coatings for SmCo2:17 high temperature magnets at temperatures up to 550°C. IEEE Trans Magn 2004; 40: 2928–2930.10.1109/TMAG.2004.829323Search in Google Scholar
Chen CH, Huang MQ, Foster JE, Monnette G, Middleton J, Higgins A, Liu S. Effect of surface modification on mechanical properties and thermal stability of SmCo high temperature magnetic materials. Surf Coat Technol 2006; 201: 3430–3437.10.1016/j.surfcoat.2006.07.233Search in Google Scholar
Dong Z, Peng X, Guo Zh, Li W, Wang F. The effect of a surface Cr film on the oxidation of SmCo-based magnetic alloy at 700°C. Corros Sci 2013; 77: 113–117.10.1016/j.corsci.2013.07.033Search in Google Scholar
Feng H, Chen H, Guo Zh, Yu R, Li W. Twinning structure in Sm(Co, Fe, Cu, Zr)z permanent magnet. Intermetallics 2010; 18: 1067–1071.10.1016/j.intermet.2010.02.008Search in Google Scholar
Feng DY, Liu ZW, Wang G, Zheng ZG, Zeng DC, Li Z, Zhang GQ. Zr and Si co-substitution for SmCo7 alloy with enhanced magnetic properties and improved oxidation and corrosion resistances. J Alloys Compd 2014; 610: 341–346.10.1016/j.jallcom.2014.05.081Search in Google Scholar
Fidler J, Schrefl T, Hoefinger S, Hajduga M. Recent developments in hard magnetic bulk materials. J Phys Condens Matter 2004; 16: S455–S470.10.1088/0953-8984/16/5/007Search in Google Scholar
Goll D, Kronmüller H. High-performance permanent magnets. Naturwissenschaften 2000; 87: 423–438.10.1007/s001140050755Search in Google Scholar
Guruswamy S, Park SM, Hirth JP, Rapp RA. Internal oxidation of Ag-In alloys: stress relief and the influence of imposed strain. Oxid Met 1986; 26: 77–100.10.1007/BF00664274Search in Google Scholar
Gutfleisch O. High temperature samarium cobalt permanent magnets. In: Liu JP, Fullerton E, Gutfleisch O, Sellmyer DJ, editors. Nanoscale magnetic material and applications. New York: Springer, 2009: 337–372.Search in Google Scholar
Gutfleisch O, Müller KH, Khlopkov K, Wolf M, Yan A, Schäfer R, Gemming T, Schultz L. Evolution of magnetic domain structures and coercivity in high-performance SmCo2:17-type permanent magnets. Acta Mater 2006; 54: 997–1008.10.1016/j.actamat.2005.10.026Search in Google Scholar
Gutfleisch O, Willard MA, Brück E, Chen CH, Sankar SG, Liu JP. Magnetic materials and devices for the 21st century: stronger, lighter, and more energy efficient. Adv Mater 2011; 23: 821–842.10.1002/adma.201002180Search in Google Scholar
Handstein A, Yan A, Martinek G, Gutfleisch O, Müller KH, Schultz L. Stability of magnetic properties of Sm2Co17-type magnets at operating temperatures higher than 400°C. IEEE Trans Magn 2003; 39: 2923–2925.10.1109/TMAG.2003.815748Search in Google Scholar
Jiang CB, An SZ. Recent progress in high temperature permanent magnetic materials. Rare Met 2013; 32: 431–440.10.1007/s12598-013-0162-6Search in Google Scholar
Kardelky S, Gebert A, Gutfleisch O, Handstein A, Wyss U, Schultz L. Corrosion behavior of Sm-Co-based permanent magnets in oxidizing environments. IEEE Trans Magn 2004; 40: 2931–2933.10.1109/TMAG.2004.829195Search in Google Scholar
Kardelky S, Gebert A, Gutfleisch O, Hoffmann V, Schultz L. Prediction of the oxidation behavior of Sm-Co-based magnets. J Magn Magn Mater 2005; 290–291: 1226–1229.10.1016/j.jmmm.2004.11.408Search in Google Scholar
Kodentsov AA, Van Dal MJH, Cserháti C, Daróczi L, Van Loo FJJ. Permeation of nitrogen in solid nickel and deformation phenomena accompanying internal nitridation. Acta Mater 1999; 47: 3169–3180.10.1016/S1359-6454(99)00194-9Search in Google Scholar
Liu S. Recent developments in high-temperature permanent magnet materials. In: Liu Y, Sellmyer DJ, Shindo D, editors. Handbook of advanced magnetic materials. New York: Springer, 2006: 1329–1377.Search in Google Scholar
Liu LL, Jiang CB. The improved oxidation resistance of Si-doped SmCo7 nanocrystalline magnet. Appl Phys Lett 2011; 98: 252504–1–3.10.1063/1.3602321Search in Google Scholar
Liu LL, Jiang CB. Oxidation resistance and magnetic properties of SmCo7-xSix permanent magnetic alloys. J Supercond Nov Magn 2012; 25: 131–135.10.1007/s10948-011-1276-4Search in Google Scholar
Liu JF, Walmer MH. Thermal stability and performance data for SmCo2:17 high-temperature magnets on PPM focusing structures. IEEE Trans Electron Dev 2005; 52: 899–902.10.1109/TED.2005.845868Search in Google Scholar
Liu S, Hoffman EP, Brown JR. Long-term aging of Sm2(Co,Fe,Cu,Zr)17 permanent magnets at 300 and 400°C. IEEE Trans Magn 1997; 33: 3859–3861.10.1109/20.619595Search in Google Scholar
Liu JF, Marinescu M, Vora P, Wu SX, Harmer MP. Effect of temperature and vacuum on the magnetic properties and compositional changes in high temperature Sm-Co magnets. J Appl Phys 2009; 105: 07A737-731–737.10.1063/1.3072764Search in Google Scholar
Livingston JD, Martin DL. Microstructure of aged (Co, Cu, Fe)7Sm magnets. J Appl Phys 1977; 48: 1350–1354.10.1063/1.323729Search in Google Scholar
Ma BM, Liang YL, Bounds CO. The effects of intrinsic coercivity on the thermal stability of Sm(Co0.70Fe0.21Cu0.06Zr0.03)7.6 sintered magnets up to 450°C. J Appl Phys 1997; 81: 5612–5614.Search in Google Scholar
Mao S, Yan M, Nie X, Sun K, Jiang J, Song Z. Evolution and effects of surface degradation layer of Sm2Co17 magnets at high temperatures. J Appl Phys 2014; 115: 043912–1–7.10.1063/1.4862857Search in Google Scholar
Ojima T, Tomizawa S, Yoneyama T, Hori T. Magnetic properties of a new type of rare earth magnets Sm2 (Co, Cu, Fe, M) 17. IEEE Trans Magn 1977; 13: 1317–1319.10.1109/TMAG.1977.1059703Search in Google Scholar
Palumbo M, Curiotto S, Battezzati L. Thermodynamic analysis of the stable and metastable Co-Cu and Co-Cu-Fe phase diagrams. Calphad 2006; 30: 171–178.10.1016/j.calphad.2005.10.007Search in Google Scholar
Pauw VD, Lemarchand D, Malandain JJ. A structural and kinetic study of the oxidation of the intermetallic Sm2(Fe,Co)17 compound for permanent magnets. J Magn Magn Mater 1997; 172: 269–276.10.1016/S0304-8853(97)00148-0Search in Google Scholar
Pragnell WM, Williams AJ, Evans HE. The oxidation of SmCo magnets. J Appl Phys 2008; 103: 07E127-1-3.10.1063/1.2830559Search in Google Scholar
Pragnell WM, Evans HE, Williams AJ. The oxidation kinetics of SmCo alloys. J Alloy Compd 2009; 473: 389–393.10.1016/j.jallcom.2008.05.083Search in Google Scholar
Pragnell WM, Evans HE, Williams AJ. Oxidation protection of Sm2Co17-based alloys. J Alloys Compd 2012; 517: 92–97.10.1016/j.jallcom.2011.12.031Search in Google Scholar
Rabenberg L, Mishra RK, Thomas G. Microstructures of precipitation-hardened SmCo permanent-magnets. J Appl Phys 1982; 53: 2389–2391.10.1063/1.330867Search in Google Scholar
Ray AE, Liu S. Recent progress in 2:17-type permanent magnets. J Mater Eng Perform 1992; 1: 183–192.10.1007/BF02648616Search in Google Scholar
Wagner C. Rektionstypen bei der oxidation von legierungen. Z Elektrochem 1959; 63: 772–782.Search in Google Scholar
Walmer MS, Chen CH, Walmer MH. A new class of Sm-TM magnets for operating temperatures up to 550°C. IEEE Trans Magn 2000; 36: 3376–3381.10.1109/20.908807Search in Google Scholar
Wang Q, Zheng L, An S, Zhang T, Jiang C. Thermal stability of surface modified Sm2Co17-type high temperature magnets. J Magn Magn Mater 2013; 331: 245–249.10.1016/j.jmmm.2012.11.013Search in Google Scholar
Wang X, Peng X, Zhao H, Guo Zh, Li W, Wang F. High temperature oxidation and its induced coercivity loss of a 2:17 type SmCo-based magnet. J Appl Phys 2015; 117: 093902.10.1063/1.4913876Search in Google Scholar
Xiong XY, Ohkubo T, Koyama T, Ohashi K, Tawara T, Hono K. The microstructure of sintered Sm(Co0.72Fe0.20Cu0.055Zr0.025)7.5 permanent magnet studied by atom probe. Acta Mater 2004; 52: 737–748.10.1016/j.actamat.2003.10.015Search in Google Scholar
Yang Z. The mechanism of high temperature oxidation of a SmCo-based magnetic alloy. PhD thesis, University of Chinese Academy of Sciences, 2013.Search in Google Scholar
Yang Z, Peng X, Feng Q, Guo Zh, Li W, Wang F. The mechanism of high temperature oxidation of a SmCo-based magnetic alloy. Corros Sci 2012; 61: 72–82.10.1016/j.corsci.2012.04.028Search in Google Scholar
Yang Z, Peng X, Feng Q, Zhao H, Wang F, Guo Zh, Li W. High temperature oxidation and protection of a Sm2(Co,Fe,Cu,Zr)17 alloy. Oxid Met 2013a; 80: 73–81.10.1007/s11085-013-9371-5Search in Google Scholar
Yang Z, Peng X, Guo Zh, Li W, Wang F. Internal oxidation of Sm(CobalFe0.22Cu0.08Zr0.02)7.5 alloy at 700°C. Corros Sci 2013b; 70: 260–267.10.1016/j.corsci.2013.01.038Search in Google Scholar
Zhao H. Effect of Cr2O3 and Al2O3 films on the high temperature oxidation of 2:17-type SmCo-based permanent magnets. PhD thesis, University of Chinese Academy of Sciences, 2015.Search in Google Scholar
Zhao J, Peng X, Wang Y, Wang F. Plasma nitridation of a novel Ni-10.8 wt.% Cr nanocomposite. Acta Mater 2007; 55: 3193–3201.10.1016/j.actamat.2007.01.018Search in Google Scholar
Zhao H, Peng X, Feng Q, Guo Zh, Li W, Wang F. A Cr2O3-deposited Sm(CobalFe0.22Cu0.08Zr0.02)7.5 magnet with increased oxidation resistance at 700°C. Corros Sci 2013a; 73: 245–249.10.1016/j.corsci.2013.04.010Search in Google Scholar
Zhao H, Peng X, Yang Z, Guo Zh, Li W, Wang F. Effect of a thin Cr2O3 film on oxidation at 600°C of a Sm(CobalFe0.22Cu0.08Zr0.02)7.5 alloy. Surf Coat Technol 2013b; 226: 22–26.10.1016/j.surfcoat.2013.03.031Search in Google Scholar
Zhao H, Peng X, Feng Q, Guo Zh, Li W, Wang F. Effect of a thin Al2O3 film on high temperature oxidation of a Sm(Co0.68Fe0.22 Cu0.08Zr0.02)7.5 alloy. Corros Sci 2014; 88: 133–140.10.1016/j.corsci.2014.07.028Search in Google Scholar
©2015 by De Gruyter